1. Field of the Invention
The present invention relates to an inkjet recording apparatus and a method for detecting discharge defects, and more particularly to technology for detecting discharge defects in nozzles that discharge ink droplets.
2. Description of the Related Art
In recent years, inkjet recording apparatuses (inkjet printers) serving as recording apparatuses that print/record images or the like taken by digital still camera have become widely distributed. Inkjet recording apparatuses have a plurality of recording elements in the head, the recording head is moved to scan the recording medium while ink droplets are discharged from the recording elements to the recording medium, the recording medium is conveyed by a single line when one line of image has been recorded on recording paper, and an image is formed on the recording paper by repeating these steps.
There are inkjet printers that use a short serial head and record images while causing the head to scan in the width direction of the recording medium, or those that use a line head in which recording elements are arrayed across the entire range of one side of the recording medium. In printers in which a line head is used, images can be recorded on the entire surface of the recording medium by scanning the recording medium in the direction orthogonal to the array direction of the recording elements. In printers in which a line head is used, a carriage or another conveyance system for moving the short head back and forth is unnecessary, and complex scanning control for the carriage movement and recording medium is not required. Also, the recording medium alone moves, so recording speed can be increased in comparison with printers in which a serial head is used.
In inkjet printers, some of the large number of nozzles sometimes no longer discharge ink for some reason, and the amount of ink discharged (the size of the dot deposited onto the recording paper) or the flight direction (droplet deposition position) becomes defective. The defective discharge of such nozzles causes the quality of recorded images to be degraded, so a countermeasure thereto is required.
Conventionally, known methods for detecting discharge defects in nozzles include a method for measuring a printed test pattern, a method for measuring an actual print job (the printed result of a target image that actually requires printing output), and a method for measuring the characteristics (resistance and other physical properties) during discharge inside the head.
In the inkjet recording apparatus and inkjet recording method disclosed in Japanese Patent Application Publication No. 2001-315318, non-discharge nozzles are identified by detecting drive voltage changes via the ink on the print head substrate by means of a detection electrode disposed inside the recording head.
The inkjet recording apparatus cited in Japanese Patent Application Publication No. 6-24008 forms a continuous line composed of all the nozzles of one head in a position in which a plurality of heads do not interfere with each other, and optically or electrically detects the existence of intermittent portions in the line thereof.
In the method and device for manufacturing a color filter cited in Japanese Patent Application Publication No. 9-101410, detection is performed based on the state when ink discharged from an inkjet head passes through a laser beam.
Nevertheless, the method for measuring a printed test pattern requires that a special purpose test pattern be printed separately from a target image that is actually to be printed. With a simple pattern, there is a drawback in that the results are affected by measurement position errors, and it is difficult to detect discharge-defective nozzles. Furthermore, there is a drawback in that the results are affected by the output variability of the line sensors that image the test pattern.
In the case of the method for measuring an actual print job, there is a drawback in that it is difficult to determine whether the actual print job is the original image content or whether it is an image defect due to a defective nozzle, and it is difficult to accurately identify discharge-defective nozzles due to the effect of measurement position errors because the actual print job, which is the measurement object, is commonly a complex image. Also, in the same manner as in the above test pattern, the results are affected by variability in the line sensors.
In the inkjet recording apparatus and inkjet recording method disclosed in Japanese Patent Application No. 2001-315318, non-discharge due to bubbles becoming intermixed in the nozzle can be detected, but non-discharge due to adhering foreign matter or other causes cannot be detected.
The inkjet recording apparatus cited in Japanese Patent Application Publication No. 6-24008 requires trial discharge paper, and paper is wasted.
In the method and device for manufacturing a color filter cited in Japanese Patent Application Publication No. 9-101410, time is required for detection when the number of nozzles has increased. Also, light-emitting diodes and photodetectors must be disposed under the nozzle, and a long head must be provided with a standby mechanism.